Abstract
Background
The magnitude of the risk of venous thromboembolism (VTE) after SARS-CoV-2 vaccines
is debated.
Methods
We included patients with a first VTE in 2021 and controls from a sample of Dutch
citizens. Participants completed a questionnaire on VTE risk factors and vaccination,
with data linked to Statistics Netherlands. Odds ratios (OR) with 95% confidence intervals
(95%CI) expressed the relative rate of VTE within 28 days post-vaccination, adjusted
for age, sex, BMI, month of index date, and major VTE risk factors (COVID-19, surgery,
cancer, and immobilization). Using previously reported age-stratified VTE incidences,
we estimated vaccination's net impact by comparing the number of events attributed
to vaccination and prevented by vaccine-induced protection against COVID-19-associated
VTE.
Results
We included 779 VTE patients and 5,311 controls. mRNA vaccines were not associated
with VTE risk (BNT162b2 [Pfizer- BioNTech] vaccine OR 1.0, 95%CI 0.7–1.3; mRNA-1273
[Moderna] vaccine OR 1.4, 95%CI 0.8–2.4). Vector-based vaccines were associated with
VTE risk (AZD1222 [AstraZeneca]: OR 1.5, 95%CI 1.0–2.5; Ad26.COV2.S [Johnson & Johnson]:
OR 2.9, 95%CI 0.9–9.2). Excluding participants with major VTE risk factors, risks
changed (BNT162b2: OR 1.5, 95%CI 1.1–2.1; mRNA-1273: OR 0.8, 95%CI 0.3–2.3; AZD1222:
OR 2.0; 95%CI 1.0–3.9; and Ad26.COV2.S: OR 3.4; 95%CI 0.7–15.5). We estimated that
SARS-CoV-2 vaccines contributed to approximately 700 VTEs but prevented approximately
3,700 VTEs.
Conclusion
SARS-CoV-2 vaccines are associated with VTE, with varying risks between types of vaccines,
and by sex and age. On a population level, in the Netherlands in 2021, SARS-CoV-2
vaccination resulted in a net benefit for the number of VTE events.
Keywords
venous thrombosis - SARS-CoV-2 vaccines - case control - population attributable fraction
